Method of making flexible fiberoptic bundles

ABSTRACT

A flexible fiberoptic bundle of light-conducting multifibers wherein each multifiber comprises a plurality of fused together individually glass-clad glass monofilaments having overcladdings of glass along their respective lengths. The overcladdings are removed throughout at least intermediate portions of the lengths of each multifiber in the fused bundle to free corresponding portions of the glass-clad glass monofilaments whereby both the flexibility of the bundle and its resistance to fiber breakage are enhanced.

TTfI hii-ed STQU "Car enter 145 20, 1974 1 METHOD OF MAKING FLEXIBLE3,033,731 /1962 C616... /4 x FIBERQPTIC BUNDLES 3,554,721 1/1971 Gardner65/4 7 3,567,549 3/1971 Hoffmeister et al 65/4 X 1 lnventorz' rg J-Carpenter, southbndge, 3,530,775 5/1971 Siegmund 65/4 1x Mass. 1 73,615,313 10/1971 P1166 61 65 4 3,624,816 11/1971 s1 k t 1.... 65/4x{73] Asmgnee: 0PM! P 3,669,772 6/1972 61221 65/4 SOulhbndge, Mass-3,674,452 7 1972 Strack.... 65/4. 3,690,853 9/1972 Law l .m: 65/4- {21}APPL N01? 7 Primary Examiner-Stephen .l. Lechert, Jr.

Related us. 4 116611611 061 Division of Sen abandoned,

u. s. c1 156/155, 65/4, 156/167, 156/168, 156/173,156/174,156/175,156/180, 156/296 161. c1 6326 31/00 Field 6: Search 156/180, 174, 296,1-73, ,1. 156/155, 167,163, 65/4 References Cited UNITED STATES PATENTS3,004,368 10/1961 Hicks 350/9613 Attorney, Agent, or Firm-William C.Nealon 57 ABSTRACT,

A flexible iiberoptic bundle-of light-conducting multifibers whereineach multifiber comprises a plurality of fused together individuallyglass-clad glass monofilaments having overcladdings of glass along theirrespective lengths. The overcladdings are removed throughout at leastintermediate portions of the lengths of each multifiber in the fusedbundle vto free corresponding portions of the glass-clad glassmonofilaments whereby both the flexibility of the bundle and itsresistance to fiber breakage are enhanced.-

6 Claims, 6 Drawing Figures I Pmmm samzm a' FIG. 5

INVENTOR. GEORGE ,d, CARPENTER ATTORNEY 3,830,667 1 l 2 METHOD OF MAKINGFLEXIBLE FIBEROPII suitably flexible for the winding of endless ribbonsis of BUNDLES exceptionally large cross-sectional size, e.g., greater IThis is a division, of application Ser. No. 97,7 l9,tiled Dec. 14, 1970,now abandoned.

BACKGROUND oFrIIE INVENTION l, Field of the Invention 1 V Fiber opticswith particular reference to flexible image-transmitting fiber bundles.

2.. Description of the Prior Art In dealing more particularly with themanufacture of flexible image-transmitting or coherent fiberopticbundles, usually called fiberscopes," there is the longstanding need foreasier and more economical fabrication procedures, improvement incoherency (i.e.,

image resolving capabilities of the finished bundle),

greater bundle strength and a reduction of the adverse effect of fiberbreakage upon image definition.

The foregoing has, to some extent, been accomplished by US. Pat. No.3,033,731, but not entirely without problems. g in seeking greatercoherency through better fiber alignment and bundle packing fraction itis necessary to turn to the use oflarger fibers which may, of course,

be multifibers. The use of larger fibers, however, renders finishedbundles less flexible and more susceptible to breakage. Adding to this,the breaking of a large fiber (multifiber), leaves a correspondinglylarge void or non-transmitting areain the bundle. Thus, as fiber size isincreased, degradation of transmitted optical images resulting fromfiber breakage increases by an order of magnitude corresponding to theincrease in fiber size.

The present invention, in dealing with the manufacture of flexiblefiberoptic bundles, particularly of large format, relates to matters ofavoiding the aforementioned problems of bundlefragility and opticalimage degradation resulting from fiber breakage by minimizing both.Greater than usual fiber alignment and bundle packing fraction attendedby improved bundlecohen ency and optical image resolution is achieved.

SUMMARY OF THE INVENTION The foregoing objectives are accomplished byutilizing, as much as possible, the flexible fiberoptic bundlemanufacturing technique of US. Pat. No. 3,033,731 which obviates some ofthe earlier problems of fiber hand-packing and aligning operations. Inthis regard, a

than 60 microns in thickness, so as to offer the important advantage ofeasy and accurate side-by-side alignment of convolutions thereof in thewinding operation as well as exceptional ease in handling of the ribbonsin making the fiber bundle assembly as outlined hereinabove.

- The bundle, however, being relatively inflexible and fragile at thisstage, is prepared for leaching. Its opposite endsare coated with anacid-resistant plastic, wax or the like and the remaining intermediateportion of the length of the bundle is exposed to a glass leachingmedium, e.g., hydrochloric acid. The'leaching medium,

in being free to circulate in between and around the 'multifibers,readily effects removal of the overclad- .dings of the monofilaments ofeach multifiber. This I greatly increases the flexibility of thefiberoptic bundle Q and correspondingly reduces image degradationresulting from accidental breakage of individual loose fibers(monofilaments) of the bundle. Thus, large losses of image definitionwhich would ordinarily result from individual multifiber fiber breakageare avoided.

.While leached fiberoptic bundles per se, are known (e.g., as shown inUS. Pat. No. 3,004,368) the fiber aligning and packing techniques insuch cases have not been entirely satisfactory, particularly when theresulting bundles are required to transport optical images. Furthermore,there has been a definite limitation as to the thickness orcross-sectional size of a bundle which can be properly and efficientlyleached to free its fibers without effecting damage thereto. This hasbeen overcome by the present invention wherein large format fiberbundles of individually flexible multifibers are leached to disconnectrespective monofilament ele ments of each multifiber.

The invention will be more clearly understood by reference totheifollowing detailed description when taken in conjunctionwith theaccompanyingdrawing. DESCRIPTION or THE DRAWINGS FIG. 1 diagrameticallyillustrates a proposed technique for making overclad glass-clad fiberfrom which multifiber may be produced according to the presentinvention; I

FIG. 2 diagrametically illustrates a technique for producing-an endlessribbon of a multifiber made up of a plurality of the aforementionedoverclad glass-clad cal opposite endfaces of the resulting flexiblefiberoptic bundle. I

in accordance with the'present invention, however, the multifiber usedto form each of the aforementioned endless fiber ribbons is comprised ofa preselected a ja glass fibers;

FIG. 3 diagrametically illustrates an assembly of the endless multifiberribbons from which a flexible bundle may beformed;

FIG. 4 illustrates the type of flexible fiber bundleresulting fromcutting transversely through the assembly of FIG. 3, opposite ends ofthe bundlein this case are shown as having protective coveringsthereover;

FIG. 5 is a greatlyenlarged fragmentary, partially cross-sectionedelevational view of one end of the fiber bundle shown in FIG. 4; and

FIG. 6 is a similarly greatly enlarged elevational view 7 of the samebundle followingtreatment thereof to enhance the flexibility of thebundle and its resistance to breakage according to principles of thepresent inven tion.

DESCRIPIIQN OF PREFERRED EMBOD1MENTS Referring more particularly toFIGS. 1-3, the operat'ions illustrated therein represent a technique forforming a flexible bundle of optical fibers as follows:

A monofilament is formed of a rod and tube assembly 12 by the well-knownpractice of heating and drawing the assembly through a suitable heatingelement 14. ln the present case, assembly 12 is comprised of'a rod 16 ofhigh refractive index core glass, an inner intermediate sleeve 18 ofcladding glass having a relarnaterial having a coefficient of thermalexpansion and melting temperature compatible with the core and claddingmaterials 16 and 18. Exemplary leachable materials are borosilicateglass or aluminum which may be conducting core of high refractive indexglass 16, a first cladding of relatively low refractive index glass 18and, additionally, a unique overcladding 22 of the aforementionedweathering or leachable material 20. A plurality of sections 24 ofmonofilament 10 are cut or bro.- ken away from the monofilament andbundled together as a boule 26 (FIG. 2) from which a multifiber 28 isdrawnthrough heating element 14. For purposes of illustration, boule 26is shown as being three fiber diameters wide whereby the multifiber 28comprises a fused together rectangular-array of nine monofilaments(sections 24). Any desired greater or lesser number of monofilaments(sections 24) may be used to form boule 26 and multifiber 28.

Fabrication of the'ultima-te flexible bundle ofoptical fibers isaccomplished by winding multifiber 28 on a suitable former, e.g. drum20, to produce endless ribbon 32 having a preselected number of tightlypacked convolutions 34. These convolutions may be wound vertically, oneover another, or horizontally, as shown. A plurality of similar ribbonsare wound, removed from the winding drum and stacked together inaccurately extent of the individual flexibility of each multifiber 28.

'- Each length of multifiber 28, being formed of a plurality of fusedtogether monofilaments is, by compaiison to the size and flexibility ofeach monotilament.-rela- V tively rigid and similarly relatively fragilein bending.

- Thus, the present invention involves further processing tively lowindex of refraction and an outer tube of 'acid-leachable fweathering"glass or metallic casing 1 0' of bundle 42 wherewith, as an objective,the bundle is rendered considerably more flexible and, similarly,considerably less fragile. This isachieved by leaching overcladdings 22of materials 20 of the individual monofilaments in the bundle away fromthe flexible intermediate sections of their respective lengths.

Since the connected together integrity of opposite ends 38 and 40 ofbundle 42 must be preserved so that these ends may ultimately becomelight-receiving and I light-emitting opposite ends of the bundle,coverings 44 and 46 of plastic, wax or other materials which areresistant to acid are applied to bundle 42 over these ends 38 and 40(H0514 and 5). These coverings, being of a material selected for itsinsolubleness in acid or other leaching solutions may be applied bypainting, dipping or taping of ends 38 and 40 of the bundle.

Referring more particularly 'to FIG. 5 which is a greatly enlargedfragmentary elevational view of one end of bundle 42, it can be seenthat, prior to' leaching of the intermediate portion of the bundle, itsmultilibers 28 eachcomprise a plurality of fused together superimposedrelationship with each other throughout a short portion .1 (FIG. v3:) oftheir corresponding lengths. These ribbons 32"are cemented, fused orotherwise secured together in portions .r thereof and sawn or otherwisecut, e.g., along line 36, to form opposite ends 38 and of flexible fiberbundle 42 (see H6. 4) which results from opening the assembly of ribbonsafter cutting. The ends 38 and 40 of bundle 42 are usu ally subsequentlyoptically finished as light-receiving and light-emitting opposite facesrespectively of the bundle. Those interested in greater detailsconcerning the technique of 3 forming optical fiber imagetransrnitti'ngbundles of endless fiber ribbons, as briefly described hereinabove, mayrefer to US. Pat. No. 3,033,731.

Referring now to flexible fiber bundle 42 of FIG. 4, it should beunderstood that the term flexible" is used res'ervedly at this point inthe process ofthe present ingether. Accordingly, the bundle is flexibleonly to the monofilarnents which are all fixedly secured togetherbeneath covering 44, and likewise beneath covering 46 (FIG. 4).lntermediately of these coverings, however,

they are individually flexible but only to an extent lim-.

ited by their relatively large cross-sectional size.

Enhancing the flexibility of bundle 42 and correspondingly decreasingits fragility according to principles of this invention, the bundle,with coverings .44 and V 46, is immersed in a bath of a preselectedleaching solution such as 5 percent (by volume) hydrochloric acidmaintained at a temperature of approximately 65 C. This solution, ofcourse, is only useful when the overcladdi'ngs 22 are formed ofleachable glass. For overcladdings 22 of metal such as aluminum or itsequivalent, sodium hydroxide may be used.

,The leaching solution would be placed in a tank, dish of. suitablereceptacle, not shown, which is selected to be of a size sufficient toreceive bundle 42.

tion of bundle 42 and spaced from each other or adapted to be so spacedby movement of bundle 42 in the leaching bath by vibration of the bathor bundle or both or by pumping of the leaching bath through thesemultifibers, relatively rapid and complete separation of allmonofilaments '10 from each other by leaching of their overcladdings iseffected. Thus, large format highly flexible bundlesof optical fiberscan be readily produced according to the present invention concept. Moreparticularly, building of the large bundle format can be achieved withexceptional accu'racyin fiber alignment and packing fractionjThis beingthe result of the now possible use of large fiber (multifiber) in theinitial fabrication (before leaching) of the bundle.

, Comparing FIG. 6 with PK}. 5 wherein the same fragmentary end sectionof the bundle is shown in each case but with covering 44 removed andmonofilament 10 released in FIG. 6,'the unique results of the inventioncan be seen. ln this respect, the initial secured to--' gether integrityof end portions of the bundle is maintained, ie with Connected togethermaterials of the fiber overcladdings, while each and every rnonofilameat10 throughout the intermediate portionof the bundle is disconnected fromall other monofilaments and free to flex individually. in this way,bundle 42 is given a substantialincrease in its overall flexibilitywhich corresponds to the decrease in cross-sectional size frommu'ltifiber 28 to monofilament 10. Also, the

bundle is given a corresponding decrease in its fragility anddegradation of transmitted optical images occuring from fiber breakage.In the latter respect, the breaking of one monofilament in bundle-42(FIG. 6) will obviously affect only a relatively very small portion ofan overall image transmitted through the bundle while breakage of alarger fiber (e.g., the size of multifiber 28 in the FIG. 5) wouldaffect a considerably larger portion of such an over-allima-ge intendedto be transferred through the bundle. An intent and purpose of theinvention is to avoid the latter.

l claim: w

l. The method of making a flexible bundle of lightconducting fibershaving oppositely disposed lightreceiving and light-emitting end facescomprising:

assembling a plurality of lengths of monofilament in juxtaposedrelationship with each other as a boule,

said lengths of monofilarnent in each case comprisifig a core of glasshaving a high refractive index,

said core being clad with a layer of glass of relatively low refractiveindex and an overcladding of fusible leachable material;

heating and drawing the boule into the form of a rriultifiber whereinsaid monofilament overcladdings' are fused together as a unit; windingsaid multifiber into the form of a plurality of short portions of saidribbons to form said convolutions of multifiber into a plurality ofindividual lengths of multifiber with corresponding opposite endsthereof constituting said end faces ofsaid bundle; and leaching at leastthe major portion of all of said over- 'claddings away from allmonofilaments of all of said multifibers intermediately of said endfaces of said bundle.

2. The method according to claim 1 wherein said ribbons are fusedtogether throughout said corresponding relatively short portions oftheir respective extensions.

-3 The method according to claim 1 wherein said ribbons are cementedtogether throughout said corresponding relatively short portions oftheir respective extensions. I

4. The method according to claim 1 wherein said overcladding material isan acid-soluble glass.

5,. The method according to claim 4 wherein said glass is a silica-freecomposition.

6. The method according to claim 1 wherein said overcladdings are formedof a metallic material.

2. The method according to claim 1 wherein said ribbons are fusedtogether throughout said corresponding relatively short portions oftheir respective extensions.
 3. The method according to claim 1 whereinsaid ribbons are cemented together throughout said correspondingrelatively short portions of their respective extensions.
 4. The methodaccording to claim 1 wherein said overcladding material is anacid-soluble glass.
 5. The method according to claim 4 wherein saidglass is a silica-free composition.
 6. The method according to claim 1wherein said overcladdings are formed of a metallic material.